It is known from Japanese Patent Application No. 3863/89 to stack a plug connector on top of a receptacle connector with contact leads depending from the former entering into openings in the latter to electrically engage upright contacts disposed therein. Whereas this arrangement is engineeringly acceptable, there is an increasing need for miniaturizing such connector systems while maintaining the same function and performances. More particularly there is a strong need for such connector systems to have as low a profile as possible. Accordingly, it is now proposed to provide a connector system which minimizes the overall height of the plug and receptacle connectors when mated together.